Search

Obesity-associated inflammation is characterized by recruitment of macrophages (M[phi]) into white adipose tissue (WAT) and production of inflammatory cytokines, leading to the development of insulin resistance. The xanthones, [alpha]- and [gamma]-mangostin (MG), are major bioactive compounds found in mangosteen that are reported to have antiinflammatory and antioxidant properties. Thus, we examined the efficacy of MG to prevent lipopolysaccharide (LPS)-mediated inflammation in human M[phi] (differentiated U937 cells) and cross-talk with primary cultures of newly differentiated human adipocytes. We found that [alpha]- and [gamma]-MG attenuated LPS-induced expression of inflammatory genes, including tumor necrosis factor-[alpha], interleukin-6, and interferon [gamma]-inducible protein-10 in a dose-dependent manner in M[phi]. We also found that [alpha]- and [gamma]-MG attenuated LPS-activated mitogen-activated protein kinases (MAPK) and activator protein (AP)-1, but only [gamma]-MG reduced nuclear factor-[kappa]B (NF-[kappa]B). In addition, [alpha]- and [gamma]-MG attenuated LPS suppression of PPAR[gamma]/gene expression in a dose-dependent manner. Notably, the ability of M[phi]-conditioned media to cause inflammation and insulin resistance in primary cultures of human adipocytes was attenuated by pretreating M[phi] with [gamma]-MG. Taken together, these data demonstrate that MG attenuates LPS-mediated inflammation in M[phi] and insulin resistance in adipocytes, possibly by preventing the activation of MAPK, NF-[kappa]B, and AP-1, which are central to inflammatory cytokine production in WAT. doi: 10.3945/jn.109.120022

Preadipocyte factor 1 (Pref-1) belongs to the Notch/Delta/Serrate family of epidermal growth factor-like repeat-containing proteins. Pref-1 is highly expressed in 3T3-L1 cells but is extinguished during adipocyte differentiation. Pref-1 serves as an excellent marker for preadipocytes. Furthermore, Pref-1 is an inhibitor of adipogenesis. Constitutive expression of Pref-1 inhibits, whereas antisense Pref-1 enhances, 3T3-L1 adipocyte differentiation. We found that Pref-1 is synthesized as a transmembrane protein but processed to generate soluble forms, including a large 50-kDa soluble form and the small soluble forms. Furthermore, only the large soluble form, but not the small soluble or the transmembrane forms of Pref-1, is biologically active to inhibit adipogenesis. We recently elucidated that the 50-kDa soluble form of Pref-1 is released by an ADAM family member, tumor necrosis factor-[alpha] converting enzyme (ADMA 17). In vivo, mice lacking Pref-1 show accelerated fat deposition; conversely, mice overexpressing soluble Pref-1 in adipose tissue show a decrease in fat mass, reduced expression of adipocyte markers, and lower adipocyte-secreted factors. These findings clearly demonstrate the inhibitory effect of Pref-1 on adipogenesis in vivo.

Docosahexaenoic acid (DHA, C22:6), a (n-3) fatty acid in fish oil, has been shown to decrease body fat and fat accumulation in rodents. We investigated the direct effect of DHA on cell growth, differentiation, apoptosis, and lipolysis using 3T3-L1 adipocytes. Cells were treated with 25-200 [micro]mol/L DHA containing 0.2 mmol/L [alpha]-tocopherol or bovine serum albumin vehicle as a control. Proliferation of preconfluent preadipocytes was not affected by the DHA treatment. When added to postconfluent preadipocytes, all concentrations of DHA inhibited differentiation-associated mitotic clonal expansion (P < 0.01). Postconfluent preadipocytes demonstrated apoptosis after 48 h with 100 [micro]mol/L DHA and after 24 and 48 h with 200 [micro]mol/L DHA (P < 0.01). Differentiation was examined by Oil Red O staining and glycerol-3-phosphate dehydrogenase (GPDH) activity after DHA treatment for 6 d. DHA decreased mean droplet size and percent lipid area in a dose-dependent manner (P < 0.01). GPDH activity was also decreased by DHA treatment (P < 0.01). In fully differentiated adipocytes, DHA increased basal lipolysis compared with the control (P < 0.01). These results demonstrate that DHA may exert its antiobesity effect by inhibiting differentiation to adipocytes, inducing apoptosis in postconfluent preadipocytes and promoting lipolysis.

Compounds that target the peroxisome proliferator-activated receptors PPAR[alpha] and PPAR[gamma] are used to correct dyslipidemia and to restore glycemic balance, respectively. Because the majority of diabetic patients suffer from atherogenic lipid abnormalities, in addition to insulin resistance, ligands are required that can activate both PPAR[alpha] and PPAR[gamma]. In this study, we used chimeric PPAR[alpha]/[gamma], reporter-gene bioassays to screen herbal extracts with purported antidiabetic properties. Extracts of Astragalus membranaceus and Pueraria thomsonii significantly activated PPAR[alpha] and PPAR[gamma]. Bioassay-guided fractionation resulted in the isolation of the isoflavones, formononetin, and calycosin from Astragalus membranaceus, and daidzein from Pueraria thomsonii as the PPAR-activating compounds. We investigated the effects of these and 2 common isoflavones, genistein and biochanin A, using chimeric and full-length PPAR constructs in vitro. Biochanin A and formononectin were potent activators of both PPAR receptors ([EC.sub.50] = 1-4 [micro]mol/L) with PPAR[alpha]/PPAR[gamma] activity ratios of 1:3 in the chimeric and almost 1:1 in the full-length assay, comparable to those observed for synthetic dual PPAR-activating compounds under pharmaceutical development. There was a subtle hierarchy of PPAR[alpha]/[gamma] activities, indicating that biochanin A, formononetin, and genistein were more potent than calycosin and daidzein in chimeric as well as full-length receptor assays. At low doses, only biochanin A and formononetin, but not genistein, calycosin, or daidzein, activated PPAR[gamma]-driven reporter-gene activity and induced differentiation of 3T3-L1 preadipocytes. Our data suggest the potential value of isoflavones, especially biochanin A and their parent botanicals, as antidiabetic agents and for use in regulating lipid metabolism. KEY WORDS: * PPAR[alpha] * PPAR[gamma] * isoflavones * adipocyte differentiation

A new member of a family of proteins functioning in the regulation of lipolysis in adipose tissue has been discovered and named 'desnutrin.' Desnutrin is transiently induced by fasting and decreased by re-feeding. A close homolog, termed adiponutrin, has the opposite expression pattern, being induced by feeding and disappearing upon fasting. Desnutrin functions by acting as the first enzyme in lipolysis, hydrolyzing triglycerides to diglycerides, whereas the well-known hormone-sensitive lipase takes the diglycerides to monoglycerides and on to free fatty acids. Key words: free fatty acids, adipocytes, lipase, hormone-sensitive, perilipin, triglycerides, diglycerides, monoglycerides, desnutrin, cyclic-AMP

Conjugated linoleic acid (CLA; 18:2)is a group of isomers (mainly 9-cis, 11-trans and 10-trans, 12-cis) of linoleic acid. CLA is the product of rumen fermentation and can be found in the milk and muscle of ruminants. Animals fed CLA have a lower body fat content. The objective of this study was to establish the possible mechanisms by which CLA affects adipogenesis. 3T3-L1 is a well-established cell line that is used extensively in studying adipocyte biology. These cells typically grow in a culture medium until they reach confluence, at which time they are induced to differentiate by hormonal treatment (d 0). Treatment of 3T3-L1 cells with 25 to 100 [Mu]mol/L CLA inhibited differentiation in a dose-dependent manner, while linoleic acid treatment did not differ from DMSO-treated controls. Continuous treatment from d -2, -1, 0 or 2 to d 8 and treatment from d -2 to d 0 and from d 0 to d 2 inhibited differentiation. Differentiation was monitored morphologically (oil Red-O staining), enzymatically (reduction of activity of glycerol-3-phosphate dehydrogenase), and by northern analysis of peroxisome proliferator-activated receptor [Gamma]2, CCAAT/enhancer binding protein [Alpha] and adipocyte specific protein 2 mRNA. CLA inhibited cell proliferation of nonconfluent cells but did not affect cell division of confluent cells, as indicated by 5-bromo-2'-deoxyuridine incorporation and mitochondria metabolism. Therefore, CLA inhibited differentiation before confluence and during induction. However, cellular proliferation was only inhibited prior to induction. These results imply that fat reduction caused by CLA treatment may be attributed to its inhibition of both proliferation and differentiation of preadipocytes in animals. KEY WORDS: * adipocytes * conjugated linoleic acid * differentiation * proliferation * fatty acids

To study the effects of dietary fish oil on insulin-stimulated glucose metabolism in adipocytes of insulin-resistant rats (rats fed 50% sucrose and 30% fat), eighteen 5-wk-old Sprague-Dawley rats were fed, for 6 wk, a diet containing 30% fat as either fish oil (FO) or a mixture of vegetable and animal oils [control oils (CO)]. A third reference group was fed a standard diet (62% corn starch and 13% fat). At the end of the 6-wk period, the two experimental groups had comparable plasma glucose concentrations that were higher than that found in the reference group. FO feeding corrected the hyperinsulinemia of the experimental rats (P [less than] 0.05) to reach values in the reference group. Plasma triacylglycerol (P [less than] 0.01 ) and cholesterol (P [less than] 0.001) concentrations were also lower in rats fed FO than in those fed CO. The body weights of FO-fed rats were similar to that of CO-fed rats, but epididymal adipose tissue weight was lower (P [less than] 0.01). Adipocytes of FO-fed rats, compared with those of CO-fed rats, had high insulin-stimulated glucose transport (P [less than] 0.05), oxidation (P [less than] 0.001) and incorporation into total lipids (P [less than] 0.05). The incorporation of (n-3) polyunsaturated fatty acids in adipocyte membrane phospholipids was higher in FO-fed rats than in those fed CO (P [less than] 0.0001). Insulin action was positively correlated with the fatty acid unsaturation index in membrane phospholipids. Thus dietary fish oil has beneficial effects on insulinemia, plasma lipids and insulin-stimulated glucose metabolism in insulin-resistant slightly diabetic rats. J. Nutr. 126: 1951-1958, 1996. INDEXING KEY WORDS: sucrose feeding; insulin action; rats; adipocytes; (n-3) polyunsaturated fatty acids

A study was conducted to determine which fatty acids in plasma membranes of adipose tissue from ruminants are changed when the diet is supplemented with unsaturated fatty acids and to determine the effect of the fat supplement on adipocyte metabolism. Ten sheep were randomly assigned to two isonitrogenous diets containing either no added fat (control) or 5 g soybean oil/100 g diet. Perirenal fat was removed at slaughter, adipocytes isolated by collagenase digestion, and plasma membranes prepared by centrifugation on a Percoll gradient. Feeding soybean oil to the sheep increased (P < 0.05) linoleic acid (18:2(n-6)) concentration in subcutaneous fat and isolated adipocytes, suggesting partial escape of dietary unsaturated fatty acids from ruminal biohydrogenation. Soybean oil consumption also decreased (P < 0.05) concentrations of myristic acid, arachidonic acid (20:4(n-6)) and anteiso 17:0 in plasma membranes, but increased (P < 0.05) trans 18:1. Lipogenesis was not affected by diet, but lipolysis tended to be greater (P = 0.07) in sheep fed the soybean oil-containing diet than in those fed the control diet. In ruminants, fatty acids of ruminal origin, namely trans intermediates of biohydrogenation or branched-chain fatty acids of microbial lipid, may account for as much change in the composition of plasma membranes and in cellular metabolism as do the small quantities of unsaturated fatty acids in the diet that escape biohydrogenation.

This study examined the influence of dietary essential fatty acids on the cooperativity of isolated adipocytes and stromal-vascular cells in the biosynthesis of prostaglandins. Sprague-Dawley rats were fed either a diet rich in essential fatty acids (20% corn oil) or a diet poor in essential fatty acids (20% tallow) for 4 wk. Preparations containing primarily adipose cells (adipocytes) or stromal-vascular cells (nonfat cells) were obtained from epididymal fat pads by collagenase digestion and repeatedly washed. Prostaglandin production was evaluated in basal and epinephrine-stimulated media after incubation with either adipocytes or adipocytes + nonfat cells. Prostaglandin E2 and prostacyclin production by adipocytes + nonfat cells was dose-dependent with epinephrine stimulation in cells from rats fed both diets. Both prostaglandin E2 and glycerol release in response to epinephrine (10-100 micromol/L) stimulation from adipocytes or from adipocytes + nonfat cells were significantly higher for cells from corn oil-fed rats than for cells from tallow-fed rats. Regardless of dietary treatment, epinephrine-stimulated prostaglandin E2 and prostacyclin release from adipocytes + nonfat cells was much greater than from adipocytes. These results suggest that a diet high in essential fatty acids precipitates a higher prostaglandin E2 secretion and that nonfat cells potentiate the secretion of prostaglandin E2 and prostacyclin by adipocytes regardless of diet.

Glucocorticoid dexamethasone mediates the differentiation of preadipocytes to adipocytes by repressing the preadipose factor 1 gene.

A rare genetic mutation is linked to extreme types of obesity. Specifically, the peroxisome proliferator-activated receptor gamma (PPARgamma) gene has a mutation leading to a receptor that cannot be blocked. Previous efforts associating leptin gene mutations to obesity have not been successful. Better understanding both genetic and environmental factors of obesity will be required to combat this global malaise.

Maintaining glucose homeostasis may involve adipose, or fat cells, in addition to muscle. The role of adipose seems important in the context of orally administered glucose, while muscle is the site of glucose transport in intravenous glucose dosages. Increased fat cells are associated with a higher circulating concentration of lactose, especially in obesity. These findings challenge the traditional concept of glucose homeostasis.

We seek to discover an effective method for utilizing thermogenesis to reduce the caloric load in obese individuals. Experimental evidence indicates that nonshivering thermogenesis is the most effective cellular and biochemical mechanism known for reducing excessive adiposity. In this presentation, we describe our experiments aimed at understanding how nonshivering thermogenesis can be induced. In addition, these experiments have led to a genetic approach for the identification of variant genes that coordinate the expression of pathways of gene transcription that are associated with brown adipocyte induction. J. Nutr. 130: 3132S-3133S, 2000. KEY WORDS: * brown adipocyte * thermogenesis * quantitative trait locus * obesity * uncoupling protein * transcription factors

The major function of adipocytes is to store triacylglycerol in periods of energy excess and to mobilize this energy during times of deprivation. The short-term control of these lipogenic and lipolytic processes is carefully modulated by hormonal signals from the bloodstream, which provide an inventory of the body's metabolic state. Long-term changes in fat storage needs are accomplished by altering both the size and number of fat cells within the body because terminally differentiated adipocytes cannot divide. Alterations in the number of fat cells within the body must be accomplished by the differentiation of preadipocytes, which act as the renewable source of adipocytes. Our understanding of the events that occur during preadipocyte differentiation has advanced considerably in the last few years and has relied mainly on the use of tissue culture models of adipogenesis. This article will discuss the various models used for studying the preadipocyte differentiation process, with the mouse 3T3-L1 cell culture line described in detail. We focus on those genetic events that link effectors to induction of adipocyte gene expression. J. Nutr. 130: 3122S-3126S, 2000. KEY WORDS: * adipose tissue * differentiation * preadipocytes * transcription factors